1. Field of the Invention
The present invention relates to a technology for improving an adhesiveness of an interlayer insulating film employing an insulating material having a lower dielectric constant.
2. Description of the Related Art
In recent years, for the purpose of satisfying the increasing requirements for obtaining higher level of the integration of semiconductor devices, copper becomes to be widely employed for material of interconnects or plugs. Copper is a material, which is characterized in having lower resistance and better electromigration resistance than that of aluminum that has been conventionally employed.
Meanwhile, it is known that copper diffuses within an insulating film comprising a silicon compound or the like at a higher rate. Thus, when copper is employed for the interconnect material, it is common that the side surface and the lower surface of the copper interconnect are covered with a barrier metal and the upper surface thereof is covered with a diffusion barrier film. Conventionally, SiN and the like are widely used for the diffusion barrier film, and recently SiCN having lower dielectric constant becomes to be often employed in view of reducing the crosstalk between the interconnects (JP-A-2002-319,619, claim 5 and paragraph 0029).
However, when the diffusion barrier film is formed by using SiCN, the production yield of the vias is often reduced, or the adhesiveness between the diffusion barrier film and the underlying insulating film is often deteriorated. These features will be described below in reference to the annexed figures. FIGS. 1A to 1D show an example of a single damascene process utilizing SiCN for the diffusion barrier film.
First, a first insulating film 301 and SiO2 film 302 are deposited in sequence on a silicon substrate that includes devices such as transistors formed thereon. These deposited films are partially etched to form an interconnect trench, and thereafter a barrier metal 303 and a copper film are deposited. Subsequently, chemical mechanical polishing (CMP) processing is carried out to form a copper interconnect 304, side surface and bottom surface of which are coated with the barrier metal 303. Thereafter, a SiCN film 306, which functions as a diffusion barrier film for copper, is formed on the entire surface of the substrate, and then a second insulating film 308 is deposited thereon. Further, a resist 310 having a predetermined aperture is formed thereon (FIG. 1A).
Subsequently, the second insulating film 308 is partially etched via the mask of the resist 310 to form a via hole 312, which extends to the surface of the SiCN film 306 (FIG. 1B).
Next, the resist 310 is stripped by an oxygen plasma ashing process, and then etch back processing is conducted to remove the SiCN film 306 disposed on the copper interconnect 304 (FIG. 1C).
Thereafter, a barrier metal and a copper film are formed on the entire surface thereof, and then the portions of the copper film and the barrier metal outside of the via hole are removed by the CMP processing to form a via plug 320 that is coupled to the copper interconnect 304 (FIG. 1D).
However, it is difficult to sufficiently improve the production yield when such process is employed. More specifically, when the resist 310 is stripped off from the multi-layer structure shown in FIG. 1B via the ashing process, carbon contained in the SiCN film 306 may react with oxygen contained in the plasma, thereby damaging the SiCN film 306. Although one via hole is shown in FIGS. 1B and 1C, a plurality of via holes are simultaneously formed on the entire surface of the wafer in the practical process. Thus, at the stage after the ashing process, the thickness and the condition of the SiCN films 306 disposed on the bottom of the via holes may be different by each of the plurality of the via holes, resulting in causing over-etching in some of the via holes when the SiCN films 306 of the bottom of the via holes are etched off in the process shown in FIG. 1C. In the over-etched vias, the surface of the copper interconnect 304 is exposed to the plasma, and thus the quality of the copper film may be deteriorated such that the contact resistance with the via plug 320 is increased.
Also, sufficient adhesiveness between the SiCN film 306 and the SiO2 film 302 overlying thereof may not be obtained, and thus peeling off may be caused between these layers in the extreme case.
These defects in the contacting nature and the adhesiveness may lead to the decrease of the production yield and the deterioration of the reliability of the devices.
Meanwhile, an example of evaluating the technology of controlling the quality of the SiCN film is disclosed in the related art. In claim 1, paragraphs 0011, 0012 and 0026 and FIG. 1 of JP-A-2002-83,870, it is disclosed that, concerning SiCN employed for the etch stop, SiCN etch stop film having better etching selectivity to the underlying film and having lower dielectric constant can be obtained by controlling the number of functional groups having carbon-hydrogen bond contained in the SiCN film. That is, JP-A-2002-83,870 is directed to solve the technical problem occurred in the case where a film corresponding to the SiO2 film 302 of FIGS. 1A to 1D is replaced with a SiCN film (claim 1, paragraphs 0011, 0012 and 0026, FIG. 1, or the like of JP-A-2002-83,870). Thus, the disclosure of JP-A-2002-83,870 provides a guidance for designing the SiCN as the etch stop film, and does not provide an useful information for designing the vias or interconnect structures in the case where SiCN is employed for the diffusion barrier film. The diffusion barrier film that covers the upper surface of the metal film functions as preventing the diffusion of metals and further functions as protecting the copper surface during etching the via holes. Thus, the other view point than that of JP-A-2002-83,870 which is related to the etch stop film is necessary for designing the SiCN film utilizing as the diffusion barrier film.